Note: Descriptions are shown in the official language in which they were submitted.
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"ELECTRIC DEVICE WITH IMPROVED HEAT REMOVAL"
BACKGROUND
Technical field
[001] The present invention relates to heat removal in electric devices, such
as liquid
immersed and dry-type transformers, and parts thereof, motors, fans, or the
like.
Description of the Related Art
[002] In the transformers field, the transformer includes parts where heat is
generated, such as the core and the windings. Heat is transferred from such
parts to a
fluid surrounding them and then eventually dissipated in the environment
through a
suitable cooling system. In general, the heat removal influences the
dimensions of the
cooling system and consequently the overall costs of the transformer.
[003] Similar considerations apply in different electric devices such as
motors or
fans, wherein heat is removed by the air flowing around heat dissipating
portions
thereof, such as fins, radiators or the like.
BRIEF SUMMARY OF THE INVENTION
[004] The object of the present invention is to provide an electric device,
such as a
transformer, a motor, a fan, or the like, configured for optimizing the heat
removal, so
to reduce the overall dimensions and costs of the device.
[005] This and other objects are achieved by an electric device in accordance
with
claim 1.
[006] Dependent claims define possible advantageous embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[007] Further characteristics and advantages of the electric device according
to the
invention will be more apparent from the following description of preferred
embodiments given as a way of an example with reference to the enclosed
drawings
in which:
[008] Figure 1 shows a perspective, partially sectional, view of a transformer
according to an embodiment of the invention;
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[009] Figure 2 shows a schematic view of means for generating a turbulent flow
according to a possible embodiment of the invention;
[0010] Figure 3 shows a perspective, partially sectional, view of a
transformer
according to a further possible embodiment of the invention;
[0011] Figure 4 shows a schematic sectional view of a transformer core
according to
a possible embodiment of the invention;
[0012] Figure 5 shows a sectional view of a detail of a transformer winding
according
to a possible embodiment of the invention;
[0013] Figure 6 shows a partial perspective view of a detail of a transformer
winding
according to a further possible embodiment of the invention;
[0014] Figure 7 shows a perspective view of a conductor strand according to a
possible
embodiment of the invention;
[0015] Figure 8 shows a side view of a continuously transposed cable according
to a
possible embodiment of the invention;
[0016] Figure 9 shows a perspective view of a continuously transposed cable
according to another possible embodiment of the invention.
DETAILED DESCRIPTION
[0017] With reference to the annexed Figures, an electric device in general is
indicated
with reference 1. The electric device within the meaning of the present
invention can
include for example transformers, motors, fans, and parts thereof, such as
conductors,
a core, windings, a tank, radiators.
[0018] The electric device 1 in general comprises at least one portion
generating heat
and at least one portion for dissipating the heat generated by said heat
generating
portion. The heat is mainly generated due to electric phenomena, such as Joule
effect,
Eddy currents, hysteresis, or the like. In order to remove heat, the heat
dissipating
portion is in a heat exchange relationship, for example in contact, with a
fluid. The
fluid in general can include a liquid, such as oil, an ester or silicone, or a
gas such as
SF6 (Sulfur hexafluoride), or air. For example, in case of dry-type
transformers, heat
is removed by environmental air in contact with the transformer active part,
which
generates heat. It is however to be noted that sometimes heat is removed
through a
primary fluid and a secondary fluid. In particular, the heat generating
portion can be
in a heat exchange relationship with a primary fluid, which in turn is in a
heat exchange
relationship with the heat dissipating portion which is in a heat exchange
relationship
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with a secondary fluid. For example, in mineral oil filled transformers, the
oil flows
around the active part, which generates heat. Heat is conveyed from the
mineral oil to
the cooling system, such as radiators, heat exchangers and the like. Then heat
is
conveyed from the cooling system to the environmental fluid, such as air or
water. In
general, therefore, primary fluids can include oil, ester, silicone, air, SF6
(Sulfur
hexafluoride), whereas secondary fluids can include air or water.
[0019] With reference for example to a transformer (Figure 1), it includes a
core 2 and
one or more windings 3 mounted to the core 2, wherein each winding comprises
at
least a low voltage winding and at least a high voltage winding. Depending on
the type
of transformer, the windings can include cast coils, foil windings, layer
windings,
helical windings, disc windings, or foil-disc windings. The transformer can be
placed
in a tank 4 filled with oil if it is of the oil immersed type, or any other
suitable fluid,
as described above. In a transformer, the heat generating portions can for
example
include: the core 2 and any metallic clamping structure thereof, the windings
3,
conductors connecting parts thereof, tank walls.
[0020] In this exemplary arrangement, the heat dissipating portions can for
example
include: internal cooling ducts 5 of the core 2, the core outer surfaces 6,
windings
internal cooling ducts 7, windings outer surfaces 8, insulated conductors 9,
internal or
external tank walls 10, fins 15.
[0021] It is to be noted that in a transformer the above heat dissipating
portions can be
in heat exchange relationship with air (for example the fins) or with oil (for
example
the internal tank walls).
[0022] According to the invention, the above cited heat dissipating portions
comprise
means for generating a turbulent flow in the fluid in contact with the heat
dissipating
portion itself. Indeed, usually the fluid in contact with the heat dissipating
portions is
laminar. If on the contrary the flow pattern is turbulent, the heat exchange
with the
fluid can be increased. As a consequence, for example it is possible to reduce
the
dimensions of heat exchanging surfaces.
[0023] The means for generating the turbulent flow can be configured in
several
manners.
[0024] In accordance with a possible embodiment, the means for generating the
turbulent flow comprise denticles 11 positioned so to be in contact with the
fluid
(Figure 2).
[0025] In accordance with a possible embodiment, the denticles comprise ribs
12
positioned so to be in contact with the fluid. The ribs 12 comprise elongated
bodies
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developing longitudinally on the heat dissipating portion surface 13. The main
longitudinal dimension of the ribs is in particular parallel to the heat
dissipating portion
surface 3, whilst ribs 12 height protrude transversally from the heat
dissipating portion
surface 13. According to a possible embodiment, the means for generating the
turbulent flow comprise a plurality of said ribs 12, preferably oriented
parallel one to
each other. Still more preferably, the ribs 12 are oriented such that their
longitudinal
direction is transversal to the fluid main flow direction, if the latter is
known (for
example in case of a forced flow around the heat dissipating portions).
According to a
possible embodiment, the ribs 12 are grouped in a plurality of groups, wherein
each
group 13 comprises a plurality of parallel ribs 12. Advantageously, in each
group 13
the ribs 12 are dimensioned differently, such that their ends define two
opposite
sinusoidal waves 14.
[0026] In accordance with another embodiment, the means for generating the
turbulent
flow comprise corrugations on a surface of the heat dissipating portions,
destined to
be in contact with the fluid. To this regard, see for example the exemplary
embodiment
shown in Figure 3. The transformer in Figure 3 comprises tank walls having
corrugations 15 extending thereon externally. The corrugations 15 can be
formed by a
plate which is bended so to assume, in transversal section, a shape
alternating peaks
16 and valleys 17. Each corrugation 15 extends preferably parallel to the next
one
developing transversally to the heat dissipating portion surface, in this case
transversally from the respective tank wall 10. It is to be noted that in this
embodiment
corrugations 15 also form fins. The same fins arrangement can be provided in a
radiator of an electric machine of different type, such as an electric motor
or a fan.
[0027] It is also to be noted that, according to further possible embodiments,
corrugations can be more generally intended also with the meaning of high
roughness
surfaces. In other words, the heat dissipating portions in general can have
high
roughness surfaces forming the means for generating the turbulent flow, which
can be
obtained in several manners, for example by tooling the surface in a suitable
manner,
by printing the surface, or by spot painting a proper insulating material on
the surface
of the heat dissipating portion. Preferably, the high roughness surfaces have
a
roughness greater than 0,2 mm, still more preferably greater than 1 mm.
Advantageously, the roughness does not exceed 6 mm.
[0028] According to a possible embodiment, the above described fins 15 in turn
can
have a high roughness with the values disclosed above.
[0029] In accordance with a further possible embodiment, the means for
generating
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the turbulent flow comprise a net made of wire to be applied on the surface of
the heat
dissipating portion or to be wrapped around the heat dissipating portion. The
net can
be arranged in a netting tape.
[0030] It is to be noted that the above cited means for generating the
turbulent flow
can be positioned on conductive surfaces (such as fins, tank walls), on
insulating
surfaces (for example paper for insulating conductors), as well as in the
cooling ducts.
[0031] In the following some further exemplary embodiments of electrical
devices
according to the invention will be described.
[0032] In figure 4 a sectional view of core 2 according to an exemplary
embodiment
is shown. According to this embodiment, the core 2 comprises a plurality of
lamination
blocks 18 arranged between two opposite clamp plates 24. Here the lamination
blocks
peripheries approximates a substantially circular shape where windings can be
wounded. Inside the core, cooling ducts 19 are formed. In particular, some
lamination
blocks 18 are spaced and the cooling ducts 19 are positioned or formed in the
spaces
20 therebetween. The cooling ducts 19 extend longitudinally inside the core
and a
cooling fluid, such as oil, flows inside them. Inside the cooling ducts 19,
means for
generating a turbulent flow in the cooling fluid, such as denticles or ribs of
the types
described above, or high roughness surfaces as discussed above, or of the
types which
will be described below, are provided. Furthermore, such means for generating
a
turbulent flow in the air or in the oil can be provided in the core outer
surfaces.
[0033] In figures 5-6 cooling ducts 19 within windings 3 are shown in two
possible
embodiments. The winding turns are separated by insulating walls 21. In a
first
embodiment (figure 5), layer windings 3 are provided and cooling ducts 19
develop
axially in or between the insulating walls 21, which can be provided with the
means
for generating turbulent flow. In a second embodiment (Figure 6), foil
windings 26 are
provided and cooling ducts 19 extend longitudinally along the insulating walls
21. The
cooling ducts 19 can be formed for example between adjacent spacing ribs 25
formed
in the insulating walls 21. The cooling ducts 19 in both embodiments are
provided
with means for generating turbulent flow in the fluid flowing in the cooling
ducts 19.
Additionally, means for generating a turbulent flow can be provided on the
windings
outer surfaces, for example in cast coils. This also improves the dielectric
performance,
in particular a higher creep strength is obtained.
[0034] In figures 7-9 conductors 22are shown. In the embodiment shown in
figure 7,
a net made of wire 23 is wrapped around the conductor 22, forming the means
for
generating the turbulent flow. In the embodiment shown in figure 8, the net 23
is
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wrapped on a continuously transposed cable, whilst in the embodiment in figure
9, a
netting tape 27 is wrapped on a continuously transposed cable. The netting
tape 27 can
carry a net, or be configured as a net itself, for example it can comprise a
plurality of
holes 28. In all the above described cases, the net and the netting tape are
configured
so to increase the surface roughness and therefore realize means for
generating a
turbulent flow.
[0035] To the above-mentioned embodiments of electric device according to the
invention, the skilled person, in order to meet specific current needs, can
make several
additions, modifications, or substitutions of elements with other operatively
equivalent
elements, without however departing from the scope of the appended claims.
